1. Field of the Invention
The present invention relates to a switch configured such that a movable contact blade is moved through a seesaw motion by a lever operation thereby to close and open the contacts of the switch.
2. Description of the Related Art
Various types of switches such as a toggle switch, for example, are in practical use in which switch contacts are turned on and off instantly through a snap action by the on/off operation of a spring-loaded lever. An example of the prior art switch of this type will be described with reference to FIGS. 10 and 11.
FIG. 10 is a diagrammatical sectional view illustrating the general construction of the prior art switch. The switch 23 comprises a generally rectangular box 11 having an open top; a neutral contact blade 12 fixed to the internal bottom surface of the box 11 generally in the center thereof; a fixed contact blade 13 fixed to the internal bottom surface of the box 11 adjacent to one end portion (left-hand end as viewed in FIG. 10) thereof; a movable contact blade 15 supported for seesaw motion by a neutral contact 12b vertically upstanding from one side edge of the neutral contact blade 12; a movable contact 16 affixed to the undersurface of the movable contact blade 15 adjacent its forward end thereof, the movable contact 16 being adapted to come into electrically and mechanically contact with a fixed contact 14 secured to the fixed contact blade 13 when the switch is turned on and to move away from the fixed contact 14 when the switch is turned off, a frame 17 covering the open top of the rectangular box 11; a sleeve 18 secured by crimping to the periphery of an opening 17a formed through the frame 17 in the center thereof; a lever 19 having a generally spherical one end portion 19b housed in the sleeve 18 and having the opposite end portion projecting out through a tapered opening 18a formed in the sleeve 18; a coil spring 21 accommodated in an axially extending housing bore 19a formed in the generally spherical one end portion (which will be referred to as inner end portion hereinafter) 19b of the lever 19; and a pushrod (or actuator) 22 having a shaft portion 22a housed in the housing or storage bore 19a and a tip portion 22b, the shaft portion 22a being resiliently urged by the coil spring 21 in such a sense as to be extended from the housing bore 19a to urge the tip portion 22b against the face of the strip-like body 15c of the movable contact blade 15.
The generally spherical inner end portion 19b of the lever 19 is greater in diameter than the tapered opening 18a in the sleeve 18 so that the lever 19 is prevented from withdrawing from the sleeve 18. In addition, the generally spherical inner end portion 19b of the lever 19, the tapered opening 18a in the sleeve 18, the coil spring 21, the pushrod 22 and the movable contact blade 15 are configured so as to cooperate to allow the instantaneous throw-up or throw-down (turning on/off) operation of the lever 19.
Further, it is to be noted that the neutral contact blade 12 and the fixed contact blade 13 have integral terminals 12a and 13a, respectively, depending from the respective strip-like bodies, the terminals 12a and 13a extending out through the bottom wall of the box 11.
FIG. 11 shows the neutral contact blade 12, the fixed contact blade 13 and the movable contact blade 15 in a perspective view as removed from the switch shown in FIG. 10. The neutral contact blade 12 comprises a strip-like body 12c secured to the bottom surface of the box 11, a terminal 12a depending from the body at one end thereof, and a generally U-shaped (channel-shaped) neutral contact 12b upstanding from one longitudinal side edge of the body and having a cutout formed in its upper end in the center thereof to define two protrusions 12b1 and 12b2. The fixed contact blade 13 comprises a strip-like body 13c secured to the bottom surface of the box 11, a terminal 13a depending from the body at one end thereof, and a fixed contact 14 affixed to the face of the body generally in the center thereof. The movable contact blade 15 comprises a strip-like body 15c, a folded portion 15a depending from the body at one end thereof, a support portion 15b including two opposed pairs of protrusions 15d1 and 15d2 extending perpendicularly and generally horizontally from the opposite longitudinal side edges of the body generally in the center thereof, and a movable contact 16 affixed to the undersurface of the body adjacent the other end thereof.
The width of the strip-like body 15c of the movable contact blade 15 is approximately equal to the length of the cutout portion of the U-shaped neutral contact 12b of the neutral contact blade 12, so that when assembled, the strip-like body 15c of the movable contact blade 15 is fitted in the cutout portion of the U-shaped neutral contact 12b with the opposite protrusions 12b1 and 12b2 engaged between the respective pairs of protrusions 15d1 and 15d2 of the support portion 15b, as shown in FIG. 10, whereby the movable contact blade 15 is positioned and supported by the neutral contact 12b of the neutral contact blade 12 for seesaw motion about the neutral contact.
While the fixed contact 14 and the movable contact 16 are typically formed of silver, they may of course be made of good electrically conductive metal such as gold. It is also to be noted that in this example the frame 17 is secured by crimping to the box 11 and that the neutral contact blade 12 and the fixed contact blade 13 are secured to the box 11 by twisting the root portions of the respective terminals 12a and 13a. 
With the switch 23 constructed as described above, it will be apparent that the throw-up and throw-down operation of the lever 19 causes the sliding movement of the tip 22b of the pushrod 22 on and along the strip-like body 15c of the movable contact blade 15 concomitant with the seesaw motion of the movable contact blade 15 so that the movable contact 16 comes into contact with the fixed contact 14 and goes away from the fixed contact 14. The operation will be described in more details with reference to FIG. 12.
FIG. 12 illustrates in diagrammatical sectional views how the movable contact 16 is moved into electrical and mechanical contact with the fixed contact 14 by the operation of the lever 19. First, as the lever 19 is maneuvered in the direction indicated by an arrow 24 (clockwise as viewed in the drawing) from the switch-off position shown in FIG. 12A, the movable contact 16 is maintained to be disconnected from the fixed contact 14 as shown in FIG. 12B until the tip 22b of the pushrod 22 passes over the neutral contact 12b. The instant that the tip 22b of the pushrod 22 has passed over the neutral contact 12b, the movable contact blade 15 is rapidly moved in a seesawing manner about the neutral contact 12b as its fulcrum in the sense to bring the movable contact 16 into contact with the fixed contact 14 under the resilient force of the coil spring 21 and concurrently the lever 19 is rapidly moved (moved by snap action) to the position shown in FIG. 12C. It is thus to be appreciated that the movable contact 16 and the fixed contact 14 are firmly contacted with each other both electrically and mechanically to turn the switch on.
Conversely, as the lever 19 is maneuvered in the counter-clockwise direction as viewed in the drawing from the switch-on position shown in FIG. 12C, the movable contact 16 is maintained to be in contact with the fixed contact 14 until the tip 22b of the pushrod 22 passes over the neutral contact 12b. The instant that the tip 22b of the pushrod 22 has passed over the neutral contact 12b, the movable contact blade 15 is rapidly moved in a seesawing manner about the neutral contact 12b as its fulcrum under the resilient force of the coil spring 21 in the sense to move the movable contact 16 out of contact with the fixed contact 14 and concurrently the lever 19 is rapidly moved (moved by snap action) to the position shown in FIG. 12A. In this way, the movable contact 16 and the fixed contact 14 are separated from each other to turn the switch off.
As is appreciated from the foregoing, the switch 23 constructed as described above is configured such that the rapid seesaw motion (snap action) of the lever 19 is effected by the extension and contraction of the coil spring 21 accommodated in the housing bore 19a in the lever 19. In other words, the arrangement is such that the quick closing and opening action of the contacts is effected irrespective of the speed at which the lever 19 is manually maneuvered.
In this regard, it should be noted that the closing and opening action is attended with such phenomena that the instant the movable contact 16 and the fixed contact 14 are brought into contact (the instant the switch is turned on), there usually flows momentarily a closing current greater than a predetermined current and that the instant the movable contact 16 and the fixed contact 14 are separated from each other (the instant the switch is turned off), there usually occurs an arc discharge. Consequently, the contacts (movable contact 16 and fixed contact 14) of this type of switch may possibly be subject to thermal deformation due to abnormal heating caused by such closing current, and further, may possibly be subject to damage by such arc discharge. For this reason, the prior art switch had the serious drawback that the contact life tended to be shortened by the closing current and the arc discharge.
It is an object of the present invention to provide a switch that has an increased contact life and superior durability.
It is another object of the present invention to provide a switch having a long contact life, which is configured to prevent a large closing current from flowing when the contacts are closed as well as to suppress an arc discharge occurring when the contacts are opened to a minimum.
In order to accomplish the foregoing objects, in one aspect of the present invention, there is provided a switch which comprises: a neutral contact blade provided with a first neutral contact and a second neutral contact; a fixed contact blade provided with a primary fixed contact and a secondary fixed contact; a primary movable contact blade supported by the first neutral contact for seesaw motion about the first neutral contact as its fulcrum and provided at one end thereof with a primary movable contact adapted to contact with and separate from the primary fixed contact; a secondary movable contact blade supported by the second neutral contact for seesaw motion about the second neutral contact as its fulcrum and provided at one end thereof with a secondary movable contact adapted to contact with and separate from the secondary fixed contact; and a pushrod integrated with a lever and adapted to slide on the primary movable contact blade and on the secondary movable contact blade on the basis of throw-up and throw-down operation of the lever to cause the primary and the secondary movable contact blades to move in a seesaw motion; whereby the secondary movable contact contacts with the secondary fixed contact before the primary movable contact contacts with the primary fixed contact, and the secondary movable contact is separated from the secondary fixed contact after the primary movable contact is separated from the primary fixed contact.
In a preferred embodiment, the primary movable contact blade comprises: a strip-like body; a folded portion depending from the body at one end thereof; a support portion including two opposed pairs of protrusions extending perpendicularly and generally horizontally from the opposite longitudinal side edges of the body generally in the center thereof; and a primary movable contact affixed to the undersurface of the body adjacent to the other end thereof, and the secondary movable contact blade comprises: a strip-like body; a folded portion depending from the body at one end thereof; a support portion including two opposed pairs of protrusions extending perpendicularly and generally horizontally from the opposite longitudinal side edges of the body toward the folded portion; and a secondary movable contact affixed to the undersurface of the body adjacent to the other end thereof; the support portion of the secondary movable contact blade being located closer to the folded portion by a distance approximately equal to the width of the body of the neutral contact blade than the support portion of the primary movable contact blade is; and the primary movable contact blade and the secondary movable contact blade being disposed in parallel with each other and supported by the first neutral contact and the second neutral contact, respectively, for seesaw motion thereabout.
In another preferred embodiment, the primary movable contact blade includes a pair of blade-like supports adapted to nip therebetween the first neutral contact and a pair of blade-like primary movable contacts adapted to nip therebetween the primary fixed contact.
Preferably, the secondary movable contact and the secondary fixed contact are formed of silver-tungsten.
With the construction as described above, the secondary movable contact of the secondary movable contact blade first contacts with the secondary fixed contact of the fixed contact blade before the primary movable contact of the primary movable contact blade contacts with the primary fixed contact of the fixed contact blade, and after the primary movable contact of the primary movable contact blade is first disconnected from the primary fixed contact of the fixed contact blade, the secondary movable contact of the secondary movable contact blade is disconnected from the secondary fixed contact of the fixed contact blade. It will thus be appreciated that both of any large closing current flow associated with the switch-on operation and any arc discharge associated with the switch-off operation may occur mainly between the secondary movable contact of the secondary movable contact blade and the secondary fixed contact blade.